The present invention relates to heat curable compositions resulting from the use of a cyclometallized platinum phosphite catalyst, an imide substituted silicone block copolymer and a polyfunctional reactive organosilicon material capable of undergoing an .tbd.SiH or .tbd.SiC.sub.2 H.sub.3 addition reaction with the imide substituted silicone block copolymer.
Prior to the present invention, room temperature vulcanizable polydiorganosiloxanes, for example, silanol terminated polydimethylsiloxanes were available in either one-package or two-package systems based on the type of moisture sensitive cross-linking agents utilized in the composition. A typical one-package system for example, is based on the use of methyltriacetoxysilane and a silanol terminated polydimethylsiloxane, as shown by Ceyzeriat, U.S. Pat. No. 3,133,891. A two-package system is shown by Nitzsche et al. U.S. Pat. No. 3,965,194. Nitzsche et al. require the blending of silanol terminated polydimethylsiloxane with a curing catalyst, such as ethyl orthosilicate in combination with dibutyltindilaurate. The two package system also requires mixing curing catalyst and silanol terminated polydimethylsiloxane prior to use.
The above described one-package and two-package room temperature vulcanizable compositions generally use a reinforcing filler, for example, a silica filler in amounts of from 5-300 parts, per 100 parts of silicone polymer, if improved tensile strength in the resulting cured product is desired.
Another procedure available for improving the toughness of cured silicone polymers is by introducing silarylenesiloxy units into the polymer chain. A copolymer is produced consisting essentially of diorganosiloxy units chemically combined with silarylenesiloxy units. Although these procedures can substantially enhance the modulus (psi) of the silicone polymer, such procedures are either uneconomic, or do not achieve the degree of toughness or elongation (%).times.tensile (psi) desired in the end product.
Heat curable compositions which can be readily vulcanized with a platinum catalyst at temperatures of 25.degree. C. or greater are described by Ryang, U.S. Pat. No. 4,517,342 assigned to the same assignee as the present invention and incorporated herein by reference. A norbornane silicone block copolymer having silicon hydride or silicon vinyl functional groups in the silicone block is used in combination with a platinum catalyst and a polyfunctional organosilicon material capable of undergoing a polyaddition reaction with such norbornane silicone block copolymer. Although the heat curable compositions of Ryang have been found to provide high strength silicone-polyimide elastomers, it often has been difficult to utilize these heat curable silicone polyimide composition in various elastomeric adhesive applications because cure of the silicone polyimide often results before it can be properly fabricated. It would be desirable, therefore, to have platinum catalyzed silicone polyimide compositions having sufficient pot life to allow the fabrication of the silicone polyimide before the platinum catalyst is activated.
The present invention is based on the discovery that certain cyclometallized platinum phosphite catalysts, as defined hereinafter, when utilized in effective amounts can provide heat curable silicone-polyimides which can be fabricated prior to cure and thereafter converted to high strength elastomers or silicone elastomeric adhesive. A one or two component heat curable polyimide composition is provided in the form of a silicone polyimide block copolymer in combination with polyfunctional organosilicon material capable of undergoing a polyaddition reaction with such silicone polyimide block copolymer.